Photo-Induced Refractive Index Changes in Bulk Semiconductors

Abstract

This article reviews the physical processes underlying photo-induced refractive index changes in bulk semiconductors. The mechanisms considered here include: 1) virtual electronic processes such as Kerr and Stark effects caused by below-band gap radiation; 2) free carrier effects which occur during and following single photon or multi-photon absorption processes and 3) thermally induced contribution. Bound carrier effects are generally weak but occur essentially instantaneously while free carrier effects are generally larger and disappear through carrier diffusion or recombination on a picosecond or longer time scale. Thermally induced effects, which decay with heat diffusion, can also be significant especially for long pulses and can remain for milliseconds. Various experimental techniques which have been used to determine refractive index dynamics in semiconductors are considered. Results of recent experiments probing the evolution of the refractive index in II–VI semiconductors on a femtosecond/picosecond time scale are used to illustrate some of the above concepts.